Consumption of dissolved oxygen in the deep Japan Sea, giving a precise isotopic fractionation factor

Concentrations and stable isotopic compositions (delta-18O) of dissolved O2 in samples collected in May 2005 from the eastern Japan Sea were measured. The O2 consumption rate and the isotopic fractionation factor during dissolved O2 consumption were obtained from the field observations by applying a simple model to the deep water. The in-situ O2 consumption rates were calculated from the apparent O2 utilization and the turnover time of deep water obtained in the previous tracer studies. The rates were 1.2-1.4 micro-mol kg-1 yr-1 in the deep water below 2000 m. The isotopic fractionation factor estimated was 0.9875 applying a Rayleigh distillation equation to the quasi-deep water of 298-3584 m. The estimated isotopic fractionation factor and the turnover time mean that delta-18O of dissolved O2 will increase with a rate of 0.05-0.06 permil yr-1 for the closed Japan Sea deep water mass.